Generally, in the development and design of a grating positioning sensor, a structural arrangement of a plurality of light sensors is adopted. For a light field generated by the grating to be sensed, this structure uses a semiconductor process to manufacture the light sensor. An accurate structure is manufactured on a single substrate and the scale of the structure is reduced at the same time. A differential signal process between the light sensors is applied to improve the ability to suppress common-mode noise. In practical application, the light sensor is generally a light-to-current type. The current generated by the light sensor is able to calculate in the circuit, the current generated by the light sensor needs to be transformed to a voltage.
However, since the process causes that the light sensors have a structure with common polarity, it is difficult for the light sensors to achieve a sensing structure with differential current. In addition, since the light sensors and the contact points thereof have the impendence property, in the direct coupling high frequency circuit, the load effect of the impendence property may influence the injection efficiency of the signal and the operation bandwidth of other circuits. Therefore, how to effectively isolate the load effect of the impendence property have become important issues.